Flash treatment of sewage sludge with the aim of increasing the energy yield

The aim of this project is to obtain a significant increase of the biodegradable part of the organic material in biological sludge in relation to an anaerobic digestion process. The procedure to follow is to expose the sludge for a momentary pressure reduction, a so called flash treatment, by which a rupture of the cell walls may take place. The cell liquid will herafter be available for degradation in the digestion process. It is expected that the potential for the new process in Denmark is an increased production of biogas, based on biological excess sludge, in the order of 700 TJ per year. The activities in the project. Study of the theory, and process modelling. Establishment of a pilot plant at the WWTP of Holbæk. With the pilot plant it will be possible to heat up, pressurise and expand the thin sludge (3-6% TS) through a nozzle system which will be in connection with a vacuum chamber. In this way a very high pressure reduction ratio is obtained. The optimal parameter-combinations of the process will be determined, primarily based on analyse of dissolved COD. With the optimal parameter setting digestion tests will be carried out (batch tests). Finally, model reactor tests will be carried out in order to investigate the biodegradability (biogas production) of the flash treated sludge under process realistic conditions. The results will be compared to not-treated sludge. Provided that the expected results are obtained it is the intention to apply for a continuation of the project in demonstration scale